The present invention relates to a method of manufacturing a pneumatic tire more particularly to a method of making a tread reinforcement being capable of reducing the tire weight.
In general, radial tires are provided in the tread portion with a breaker to reinforce the tread portion. Further, in case of high speed use especially, a band is disposed on the radially outside of the breaker.
The breaker comprises two cross plies of parallel cords, wherein the plies are disposed one upon another so that the cords of one ply are crosswise to the other ply.
Conventionally, such a breaker is made such that first a strip of rubberized unwoven cord fabric is wound and, then another strip of rubberized unwoven cord fabric whose cord inclination is crosswise is wound on the former winding. As shown in FIG. 7, each strip has a constant width La and a length more than the circumferential length of the breaker, and the circumferential ends of each strip is spliced as shown in FIG. 8. Thus, the breaker has at least two splices.
As the spliced portion becomes thicker, the tire uniformity and conicity deteriorate, and as a result, steering stability, ride comfort and the like tend to deteriorate. usually, the coating thickness (t) of the topping rubber (g) is set in a range of more than about 0.5 mm to be able to handle the strip as a continuous sheet. Thus, in the portion other than the spliced portions, the total thickness (t0) of two cross breaker plies becomes equal to the thickness of the cordxc3x972+the coating thickness (t)xc3x974 in rough, as shown in FIG. 9. This makes it difficult to reduce the tire weight.
The laid-open Japanese patent application JP-A-5-16610, discloses the use of a strip of two-axial woven cord fabric in stead of the above-mentioned two cross plies of rubberized unwoven cord fabric. In this case, a cord spacing corresponding to the cord spacing (d) of the conventional breaker becomes zero and the total thickness of the breaker may be reduced accordingly. But, as the cords substantially contact each other in their crossings, they are rubbed against each other by the pantograph phenomenon accompanying the tread deformation during running, and thus the durability tends to decrease.
It is therefore, an object of the present invention to provide a pneumatic tire in which the tire weight is effectively reduced by reducing the weight of the tread reinforcing structure, and the damage on the cords by rubbing is prevented to improve the durability, and further the uniformity, steering stability, ride comfort and the like are improved.
According to the present invention, a method of manufacturing a pneumatic tire comprises
making a rubber-coated cord-member by coating one or more cords with rubber, and
making a tread reinforcement by putting together a plurality of the cord-members around a drum into a cylindrical network of the cords, which cords make a first array of cords inclining in one direction with respect to the tire equator and a second array of cords inclining in one direction which is opposite to the cords of the first array with respect to the tire equator.